This invention relates to a process for producing an .alpha., .omega.-hydroxyfluoroalkylpolysiloxane. More particularly, this invention relates to a process for producing an .alpha., .omega.-hydroxyfluoroalkylpolysiloxane that easily controls the viscosity of an .alpha., .omega.-hydroxyfluoroalkylpolysiloxane, and a process that enables the production of an .alpha., .omega.-hydroxyfluoroalkylpolysiloxane that does not exhibit any substantial change of viscosity over time.
Conventionally, fluorosilicone compositions have been used as useful and valuable silicone fluids, since they can impart resistance to solvents and chemical, and repellency to otherwise conventional silicone compositions. A typical example of the fluorosilicone compositions is a silanol chain-stopped fluorosilicone composition, and a process for producing it is disclosed in U.S. Pat. No. 4,287,353. This process comprises the step of reacting 100 parts by weight of a methyltrifluoropropylsiloxane with a mixture of 0.005 to 0.1 parts by weight of a polymerization catalyst such as KOH or NaOH, 0.02 to 5.0 parts by weight of water, and 0.010 to 2.0 parts by weight of a polyethyleneglycol dimethyl ether as a promoter, and the step of adding a neutralizer such as hydrochloric acid or a silyl phosphate solution to obtain a fluorosilicone oil.
The '353 Patent discloses that the use of triethyleneglycol dimethyl eter, etc., as a promoter, lowers the polymerization initiation temperature, and shortens the polymerization time, and thereby decreases the amount of byproduct volatile siloxanes.
However, the process disclosed in the '353 U.S. Patent proceeds too rapidly to stop the polymerization at the desired viscosity. The more fatal defect is that the fluorosilicone oil exhibits a serious change of viscosity over time, and thus, it is impossible to store it stably for a long time.
Accordingly, it is a first object of the present invention to provide a process for producing a fluorosilicone oil that can lengthen the polymerization time while maintaining a low polymerization temperature during the polymerization period, and thereby enabling the easy production of a fluorosilicone oil having a desired viscosity.
An additional object of the present invention is to provide a process for producing a fluorosilicone oil that does not exhibit any substantial change of viscosity over time, and that can be stably stored for a long time without its viscosity being changing.
It has now been found by the inventors that the first object is attained by employing lithium hydroxide or a lithium salt of a diorganosiloxane obtained by blending and heating lithium hydroxide and a diorganosiloxane, as a polymerization catalyst, and a phthalic diorganoester and/or ortho-dialkoxybenzene, as a promoter.
It has now also been found by the inventors that the second object is attained by employing a chloroethane as a neutralizer to stop the polymerization reaction.
These and other objects of the present invention are accomplished by means of the disclosure set forth below.